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Fig. 2. Cutaway of first self-contained model of interferometer gauge.
the outer ring, which is in contact with the diaphragm, to the center of the diaphragm is directly proportional to the distance from the center of the diaphragm to the quartz backing plate; therefore, the number of fringes counted on a photographic film is directly proportional to the pressure applied. This linear relationship is, of course, a highly desirable feature for ease of calibration and interpretation of records.
Camera Details
The camera proper is of the familiar continuous moving film variety, but the special features of various models which have been developed should be mentioned.
The general scheme for film transport is the same on all models, and consists of a high-speed motor directly coupled to the take-up spool. The speed of the
motor is controlled by a governor which is mounted on an idler drum driven by the friction of the film being pulled over it. Thus the motor speed is varied to give a constant film speed as the take-up reel increases in size. On most models the film speed can be controlled from 10 to 80 ft/sec. The supply spool has an adjustable drag to keep tension on the film which supplies driving power for the governor and to keep the film in the image plane. One model which was intended for short runs has a magnetic fluid brake3 on the take-up reel which is supplied with power as soon as the driving motor circuit is broken. This camera will make as many as ten runs on a 100-ft spool of film at 80 ft/sec, and have the major part of each run at full speed.
One model is equipped with a footage counter which reveals the amount of
W. E. Buck: Pressure Recording With Interferometer Camera
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